The present invention relates to refrigerating apparatus, and particularly to refrigerating apparatus for medical use. Such refrigerating apparatus, which may be used for surgical or therapeutic use, comprises a tubular probe within which is a capillary tube along which, in use of the apparatus, flows a refrigerant fluid which evaporates at a temperature lower than room temperature, which fluid is supplied to the capillary tube in the liquid state; the refrigerant is drawn in the gaseous state from a pressurised container and flows through a thermostatic condenser by which it is liquified before it is fed to the capillary tube within the probe. The end of the capillary tube communicates with an expansion chamber at the tip of the probe and flash evaporation and expansion of the refrigerant fluid as it flows from the capillary tube into the expansion chamber causes refrigeration of the walls of the expansion chamber. The refrigerant fluid then flows back from the expansion chamber along an annular conduit between the capillary tube and a second tube which surrounds it. From the annular conduit the refrigerant flows through a valve controllable by the operator and escapes to the atmosphere.
Refrigerating apparatus of this type, which is used medically to locally freeze body tissue for therapeutic and/or surgical purposes is often referred to as a cryosurgical or cryotherapeutical insturment. Such instruments have been successfully in use for some years, mostly in the fields of gynaecology, otorhinolaryngology, dermatology and ophthalmology.
One disadvantage of known medical refrigerating instruments, however, is the difficulty of providing satisfactory thermal insulation of the refrigerated tip of the probe from the remainder of the probe. In known cryosurgical instruments the whole of the probe and even the operator's hand grip can become extremely cold, and the temperature of the probe can approach that of the refrigerating tip after long periods of continuous use.
When treating skin, the fact that the probe is at a low temperature along the whole of its length does not cause serious difficulty and when the instrument is employed in fairly wide body cavities the probe can be provided with a thermal insulating covering along its length, except for the refrigerating tip, which results in an increase in cross-sectional size of the probe.
However, for use in narrowly restricted body regions, which is necessary, for example, in the ophthalmic field when operating on the retina, an increase in cross-sectional size of the probe is inadmissible, rather this size should be reduced as far as possible. If the probe is not well insulated along its length, however, the danger arises that the sides of the probe could accidentally touch parts which are not to be refrigerated and injure them irreparably. It is therefore clear that the use of a refrigerating instrument without insulated probes for eye operations requires a very high degree of skill by the surgeon.